Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
- Subject: Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
- From: Charles Srstka <email@hidden>
- Date: Tue, 20 Apr 2004 10:03:20 -0500
On Apr 20, 2004, at 3:27 AM, Nicko van Someren wrote:
Setting aside the other considerations for a moment, as a professional
cryptographer I would strongly advise against using RSA with keys as
short as 192 bits. While I don't have exact figures to hand for 192
bit numbers it's worth noting that it is less than half the length of
the first RSA Challenge and I suspect it would take a matter of hours
to factor on a decent modern computer. According the the RSA FAQ on
factoring [1] numbers with 430 bits can be factored inside a year
using a single PC and in previous work I've shown that a single 42
unit rack of G5 X Serves can factor 512 bit keys at a rate of about
one every two weeks. As well as the more complex (to code and to
understand) sieve methods there are methods that are trivial to code
and require minimal knowledge of mathematics which will factor your
key in about 2^48 steps.
Using public key crypto is (IMHO) a great way to create software
licenses. Its use means that even if your code is reverse engineered
an attacker can not fake new licenses. That said, if the key that you
use is too short and can be factored all this security disappears. If
I were you I'd go for a much much longer key.
But there's still that issue of the registration code you generate
being way too long with a decent-sized key...
Charles
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